Magnetic gear

ABSTRACT

Embodiments of the present invention relate to magnetic gears comprising a pair of rotors magnetically coupled in a geared manner via a magnetic space harmonic generated as a consequence of varying an air gap between sets of permanent magnets.

FIELD OF THE INVENTION

Embodiments of the present invention relate to magnetic gears.

BACKGROUND TO THE INVENTION

Mechanical gearboxes are extensively used to match the operating speedof prime-movers to the requirements of their loads for both increasingrotational speed such as, for example, in a wind-powered generator orreducing rotational speed such as, for example, in an electric-shippropulsion arrangement. It is usually more cost and weight effective toemploy a high-speed electrical machine in conjunction with a mechanicalgearbox to achieve requisite speed and torque characteristics. However,white such a high-speed electrical machine in conjunction with amechanical gearbox allows high system torque densities to be realised,such mechanical gearboxes usually require lubrication and cooling.Furthermore, reliability can also be a significant issue. Consequently,direct drive electrical machines are employed in applications where amechanical gearbox cannot be used.

Several techniques of achieving magnetic gearing, using permanentmagnets, are known within the art. For example, FIG. 1 shows the mostcommonly used topology for magnetic gears. It can be appreciated thatFIG. 1 shows a magnetic gear 100 comprising a first, high-speed, rotor102 bearing a plurality of permanent magnets 104 that is magneticallycoupled, in a geared manner, to a second, low speed, rotor 106comprising a number of permanent magnets 108. A significant disadvantageof the magnetic gear 100 shown in FIG. 1 is that the topology suffersfrom a very poor utilisation of the permanent magnets since very few ofthe permanent magnets simultaneously contribute to torque transmissionat any given time. The very poor torque transmission capability haslimited the use of magnetic gearing.

The problem associated with the magnetic gear 100 of FIG. 1 is solved bythe magnetic gear 200 shown in FIG. 2. FIG. 2 shows a rotary magneticgear 200 comprising a first or inner rotor 202, a second or outer rotor204 and a number of pole pieces 206, otherwise known as an interferenceor an interference means. The first rotor 202 comprises a support 208bearing a respective first number of permanent magnets 210. In theillustrated magnetic gear, the first rotor 202 comprises 8 permanentmagnets or 4 pole-pairs arranged to produce a spatially varying magneticfield. The second rotor 204 comprises a support 212 bearing a respectivesecond number of permanent magnets 214. The second rotor 204 comprises46 permanent magnets or 23 pole-pairs arranged to produce a spatiallyvarying field. The first and second numbers of permanent magnets aredifferent. Accordingly, there will be little or no useful directmagnetic coupling or interaction between the permanents magnets 210 and214 such that rotation of one rotor will not cause rotation of the otherrotor.

The pole pieces 206 are used to allow the fields of the permanentmagnets 210 and 214 to interact in a geared manner. The pole pieces 206modulate the magnetic fields of the permanent magnets 210 and 214 sothey interact to the extent that rotation of one rotor will inducerotation of the other rotor in a geared manner. Rotation of the firstrotor 202 at a speed ω₁ will induce rotation of the second rotor 204 ata speed ω₂ where ω₁>ω₂ and visa versa.

However, the magnetic gear topology shown in FIG. 2 has thedisadvantages that it is unsuitable for high gear ratios, it isrelatively complex and has an unfavourable torque density especiallywhen higher gear ratios are required.

It is an object of embodiments of the present invention to at leastmitigate one or more of the above problems of the prior art.

SUMMARY OF EMBODIMENTS OF THE INVENTION

Accordingly, a first aspect of embodiment of the present inventionprovides a magnetic gear comprising first and second moveable membershaving associated first and second pluralities of permanent magnetsrespectively arranged such that the first and second pluralities ofpermanent magnets are separated by a varying distance that, in responseto relative movement of the first and second moveable members,magnetically couples the first and second pluralities of permanentmagnets in a geared manner via a common magnetic harmonic generated as aconsequence of the relative movement.

Advantageously, the magnetic gears according to embodiments of thepresent invention exhibit significant advantages, in terms of simplicityand torque density, especially when higher gear ratios are required ascompared to the prior art.

Other embodiments are described below and claimed in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 shows a conventional magnetic gear;

FIG. 2 shows a further conventional magnetic gear;

FIG. 3 shows a magnetic gear according to a first embodiment;

FIG. 4 shows a graph of variation in normal flux density withcircumference position of the embodiment shown in FIG. 3;

FIG. 5 illustrates a harmonic spectrum of the waveform shown in FIG. 4;

FIG. 6 depicts a magnetic gear according to a further embodiment;

FIG. 7 shows another embodiment of a magnetic gear;

FIG. 8 illustrates yet another embodiment of a magnetic gear;

FIG. 9 depicts still another embodiment of a magnetic gear;

FIG. 10 shows a graph of variation of pull-out torque with maximum airgap per metre of axial length for embodiments of the present invention;

FIG. 11 shows a preferred embodiment of a magnetic gear;

FIGS. 12( a) to (d) illustrate the operation of an embodiment of amagnetic gear;

FIG. 13 depicts circumferential variation of normal flux density clue tomovement of an intermediary rotor for a given point at the centre of astator magnet according to an embodiment;

FIG. 14 shows a magnetic harmonic spectrum of the waveform of FIG. 13;and

FIGS. 15( a) to (d) illustrate the gearing of a magnetic gear accordingto an embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 3 shows a magnetic gear 300 according to a still furtherembodiment. The magnetic gear 300 comprises an inner rotor 302, an outerrotor 304 and a stator 306. The inner rotor 302 comprises anon-cylindrical shaft 308 arrange to rotate about an axis (not shown).The outer rotor 304 comprises a number of permanent magnets 310 mountedon a flexible substrate 312. A plurality of bearings 314 are disposedbetween the inner rotor 302 and the outer rotor 304 to support relativerotation between the inner 302 and outer 304 rotors. The stator 306comprises a plurality of permanent magnets 316, mounted on a substrate318, that are magnetically coupled to the permanent magnets 310 of theouter rotor 304 to produce a geared rotation between the inner 302 andouter 304 rotors using the above described principles, that is, thecircumference of the inner rotor is at least one of shaped and rotatedat a predetermined speed to produce harmonics that couple the permanentmagnets 310 of the rotor 304 to the permanent magnets 316 of the stator306, that is, selected pole-pairs of the outer rotor permanent magnetsare coupled to corresponding pole-pairs of the stator permanent magnets.

Preferably, the inner rotor 302 is a high-speed rotor. The high-speedrotor 302 is non-circular. The high-speed rotor 302, also known as awaveform generator, is, as indicated above, shaped so as to have apredetermined profile. In the embodiment illustrated, the waveformgenerator 302 has a sinusoidal profile having a radius, r, measuredrelative to an axis of the shaft, given by

r=r _(ov) +r _(b) cos(2θ)  (1)

where r_(av) is the average radius and r_(b) is the maximum deviationfrom the average. It is worth noting that although for the embodimentshown in FIG. 3 is profile given by equation (1) is adopted any profilewhich could be approximated by r=r_(av)+r_(b) cos(nnθ), where nn is aninteger would work. Therefore, the flux-density due to the low-speedrotor magnets 310 can be written as:

$\begin{matrix}\begin{matrix}{B = {B_{m}{{\cos \left( {{pp}\; \theta} \right)}\left\lbrack {\lambda_{0} + {\lambda_{1}{\cos \left( {2\; \theta} \right)}}} \right\rbrack}}} \\{= {{B_{m}{\cos \left( {{pp}\; \theta} \right)}\lambda_{0}} + {\frac{1}{2}B_{m}\lambda_{1}{\cos \left( {\left( {{pp} + 2} \right)\theta} \right)}} +}} \\{{\frac{1}{2}B_{m}\lambda_{1}{\cos \left( {\left( {{pp} - 2} \right)\theta} \right)}}}\end{matrix} & (2)\end{matrix}$

Therefore, harmonics with pole-pairs of (pp+2) and (pp−2) are createdthat can interact with the stator magnets 316.

Gear Ratio

Writing equation (2) as a function of time gives

$\begin{matrix}\begin{matrix}{B = {B_{m}{{\cos \left( {{pp}\left( {\theta - {\omega_{ls}t}} \right)} \right)}\left\lbrack {\lambda_{0} + {\lambda_{1}{\cos \left( {2\left( {\theta - {\omega_{w}t}} \right)} \right)}}} \right\rbrack}}} \\{= {\ldots + {B_{m}\lambda_{1}{\cos \left( {{pp}\left( {\theta - {\omega_{ls}t}} \right)} \right)}{\cos \left( {2\left( {\theta - {\omega_{w}t}} \right)} \right)}}}} \\{= {\ldots + {\frac{B_{m}\lambda_{1}}{2}{\cos \left\lbrack {{\left( {{pp} - 2} \right)\theta} + {\left( {{2\omega_{w}} - {{pp}\; \omega_{ls}}} \right)t}} \right\rbrack}} +}} \\{{\frac{B_{m}\lambda_{1}}{2}{\cos \left\lbrack {{\left( {{pp} + 2} \right)\theta} - {\left( {{2\; \omega_{w}} + {{pp}\; \omega_{ls}}} \right)t}} \right\rbrack}}}\end{matrix} & (3)\end{matrix}$

where ω_(is), is the speed of the low speed rotor 304 and

-   -   ω_(w) is the speed of the high speed rotor 302 (wave-form        generator)

Therefore, in order for the harmonic of order (pp+2) to couple with thestatic field of the stator magnets 316, the following relationshipbetween the rotor speeds must hold:

$\begin{matrix}{\omega_{ls} = {- \frac{2\; \omega_{w}}{pp}}} & (4)\end{matrix}$

If the gear is designed with q=(pp−2) pole-pairs on the stator 306, therelationship, expressed in terms of such pole-pairs, between the rotorspeeds becomes:

$\begin{matrix}{\omega_{ls} = {+ \frac{2\omega_{w}}{pp}}} & (5)\end{matrix}$

It should further be noted that the magnets 310 on the low-speed rotor304 rotate with respective, different, speeds at each moment in time dueto their different positions on the sinusoidal circumference or profileof the high-speed rotor 302. Therefore, ω_(is) represents the averagerotational speed of all magnets 310 of the low speed rotor 304.

There are a number of parameters associated with the magnetic gear 300shown in FIG. 3. It should be noted that the flexible or low speed rotor304 comprises a number of pole-pairs, pp. Secondly, the stator 306comprises a number of pole-pairs, qq. Thirdly, the stator 306 has apredetermined outer radius, Ro. Fourthly, the magnets 316 on the stator306 have a predetermined radial thickness, Lpm_stat. The magnets 310 ofthe low speed rotor 304 have a predetermined radial thickness, Lpm_low.Due to the noncircular shape of the high-speed rotor 302, the radial gapbetween the permanent magnets 310 of the low speed rotor 304 and thepermanent magnets 316 of the stator 306 varies. In the embodimentillustrated, the radial air gap varies from a minimum, Gap_min, to amaximum, Gap_max. Fifthly, the back-iron 314 of the stator 306 has apredetermined radial length or thickness, Liron_stat. The dimensions ofthe above parameters for an embodiment of the harmonic gear 300 may beas given in table 1 below.

TABLE 1 Dimensions of harmonic gear in FE predictions Outer radius, Ro85 mm  Minimal length of air-gap, gap_min 1 mm Length of back-iron onstator, Liron_stat 5 mm Minimal Length of back-iron on low-speed rotor,Liron_low 5 mm Magnet thickness on stator, Lpm_stat 5 mm Magnetthickness on low-speed rotor, Lpm_low 5 mm

The number of pole-pairs, qq, on the stator 306 must be equal to (pp+2)or (pp−2), as has been deduced from equation (2), to produce torquebetween the stator and low-speed rotor magnets. To demonstrate thisfurther, FIG. 4 shows a graph 400 of the variation of normal fluxdensity, which is due to the low-speed rotor magnets 312, through or atthe centre of the stator magnets 316 with circumferential position foran embodiment of a magnetic gear 300 with pp=20 and gap_max=9.5 mm.

FIG. 5 shows a harmonic spectrum 500 of the waveform 402 shown in FIG.4. It can be seen from the harmonic spectrum 500 that the (pp+2)harmonic 502 has the largest flux density amplitude. Therefore, anembodiment of a magnetic gear with qq=(pp+2) stator pole-pairs willproduce the maximum torque for a low-speed rotor having pp pole-pairs.Table 2 compares predicted torques for embodiments of the gear when thestator has qq=(pp−2)=18 and qq=(pp+2)=22 pole-pairs.

qq=(pp−2)=18 qq=(pp+2)=22

-   -   Torque per meter 1170 Nm 3020 Nm

Table 2, Comparison between predicted torque when stator has (pp+2) and(pp−2) pole-pairs

FIGS. 6 to 9 show various magnetic gears according to embodiments of thepresent invention. The embodiments have the parameters as describedabove with reference to table 1 but with different respective values ofgap_max.

Referring to FIG. 6, there is shown an embodiment of a magnetic gear 600comprising a first rotor 602, a second rotor 604 and a stator 606. Thesecond rotor 604 comprises 40 pole pairs. The stator 606 comprises 42pole-pairs and the maximum air gap is 5.5 mm.

Referring to FIG. 7, there is shown an embodiment of a magnetic gear 700comprising a first rotor 702, a second rotor 704 and a stator 706. Thesecond rotor 704 comprises 30 permanent magnets. The stator 706comprises 32 pole-pairs and the maximum air gap is 7 mm.

Referring to FIG. 8, there is shown an embodiment of a magnetic gear 800comprising a first rotor 802, a second rotor 804 and a stator 806. Thesecond rotor 804 comprises 40 pole pair. The stator 806 comprises 22pole-pairs and the maximum air gap is 9.5 mm. This arrangement is thesame as that described with reference to FIG. 3.

Referring to FIG. 9, there is shown an embodiment of a magnetic gear 900comprising a first rotor 902, a second rotor 904 and a stator 906. Thesecond rotor 904 comprises 10 pole pairs. The stator 906 comprises 12pole-pairs and the maximum air gap is 16 mm.

FIG. 10 illustrates a graph 1000 showing the variation of pull-outtorque with maximum air gap per metre of axial length for theembodiments described with reference to FIGS. 6 to 9. A first curve 1002illustrates the torque versus maximum air gap performance for theembodiment described with reference to FIG. 6. A second curve 1004illustrates the torque versus maximum air gap performance for theembodiment described with reference to FIG. 7. A third curve 1006illustrates the torque versus maximum air gap performance for theembodiment described with reference to FIG. 3 or 8. A fourth curve 1008illustrates the torque versus maximum air gap performance for theembodiment described with reference to FIG. 9.

Referring to FIG. 11, there is a shown a magnetic gear 1100 according toan embodiment having non-coaxial or eccentric rotors that rotate aboutrespective axes, such that one axis orbits another axis.

The magnetic gear 1100 shown in FIG. 11 comprises first 1102 and second1104 stages. The magnetic gear 1100 is illustrated using two end views1106 and 1108 and a cross-sectional-axial view 1110.

The first stage 1102 comprises an input rotor 1112 having mountedthereon, via bearings 1114, an inner or first rotor 1116, also known asan intermediary rotor. The first stage 1102 also comprises a stator1118. It can be appreciated that the input rotor 1112 is coupled, in aneccentric manner, to a central shaft 1120. The intermediary rotor 1116comprises a plurality of permanent magnets 1126. The stator 1118comprises a soft magnetic material 1128 bearing a plurality of permanentmagnets 1130. Rotation of the input rotor 1112 around its axis 1124,causes the intermediary rotor 1116 to orbit the axis 1124. This, inturn, causes the intermediary rotor 1116 to rotate about its centralaxis 1122, as a result of the magnetic coupling between the pluralitiesof permanent magnets 1126 and 1130, caused by the varying radial airgapbetween them. It can be appreciated that the intermediary rotor 1116bears, at an output end, that is, in the second stage 1104 of themagnetic gear 1100, a second set of permanent magnets 1132 comprising apredetermined number of permanent magnets. The second stage 1104 of themagnetic gear 1100 comprises an output rotor 1134 bearing a plurality ofpermanent magnets 1136. The rotation of the intermediary rotor 1116around the axis 1122 causes the rotation of output rotor 1134 aroundaxis 1124 as a result of the magnetic coupling between the pluralitiesof permanent magnets 1132 and 1136 caused by the varying radial airgapbetween them. It can be appreciated that the outer rotor 1134 is mountedto a respective output portion 1138 of the shaft 1120 via a bearing1140. The output portion 1138 is coaxial with the input rotor 1112 and,therefore, shares the common axis 1124.

The contour of the intermediary rotor 1116, formulated from the centreof the stator 1118 or output rotor 1134, can be approximated as asinusoidal profile:

r=r _(av) +r _(b) cos(θ)  (6)

Therefore, the flux-density in the outer bore of the gear in stage 1 orstage 2, due to the intermediary rotor magnets 1126 or 1132, can bewritten as:

$\begin{matrix}\begin{matrix}{B_{1,2} = {B_{m}{{\cos \left( {{pp}_{1,2}\theta} \right)}\left\lbrack {\lambda_{0} + {\lambda_{1}{\cos (\theta)}}} \right\rbrack}}} \\{= {{B_{m}{\cos \left( {{pp}_{1,2}\theta} \right)}\lambda_{0}} + {\frac{1}{2}B_{m}\lambda_{1}{\cos \left( {\left( {{pp}_{1,2} + 1} \right)\theta} \right)}} +}} \\{{\frac{1}{2}B_{m}\lambda_{1}{\cos \left( {\left( {{pp}_{1,2} - 1} \right)\theta} \right)}}}\end{matrix} & (7)\end{matrix}$

where the subscripts 1 and 2 denote the 1^(st) and 2^(nd) stages of thepermanent magnets respectively.

Therefore, harmonics with pole-pairs of (pp_(1,2)+1) and (pp_(1,2)−1)are created at the outer magnets 1130 and 1136 of each stage of themagnetic gear 1100. The former harmonic is generally larger than thelatter. Hence, qq_(1,2)=pp_(1,2)+1 are been selected for realising sucha magnetic gear 1100.

Gear Ratio

Equation (7) can be written as a function of time to give:

$\begin{matrix}\begin{matrix}{B_{1,2} = {B_{m}{{\cos \left( {{pp}_{1,2}\left( {\theta - {\omega_{m}t}} \right)} \right)}\left\lbrack {\lambda_{0} + {\lambda_{1}{\cos \left( {\theta - {\omega_{i\; n}t}} \right)}}} \right\rbrack}}} \\{= {\ldots + {B_{m}\lambda_{1}{\cos \left( {{pp}_{1,2}\left( {\theta - {\omega_{m}t}} \right)} \right)}{\cos \left( {\theta - {\omega_{i\; n}t}} \right)}}}} \\{= {\ldots + {\frac{B_{m}\lambda_{1}}{2}{\cos \left\lbrack {{\left( {{pp}_{1,2} - 1} \right)\theta} + {\left( {\omega_{i\; n} - {{pp}_{1,2}\; \omega_{m}}} \right)t}} \right\rbrack}} +}} \\{{\frac{B_{m}\lambda_{1}}{2}{\cos \left\lbrack {{\left( {{pp}_{1,2} + 1} \right)\theta} - {\left( \; {\omega_{i\; n} + {{{pp}\;}_{1,2}\omega_{m}}} \right)t}} \right\rbrack}}}\end{matrix} & (8)\end{matrix}$

where ω_(m) is the speed of the intermediary rotor 1116 and

-   -   ω_(in) is the speed of the input shaft 1112 (high-speed rotor).        Stage 1: in order for the harmonic of order (pp₁+1) to couple        with the static field of the stator magnets 1130, the        relationship between the rotor speeds can be derived as follows:

$\begin{matrix}{\omega_{i\; n} = {- \frac{\omega_{i\; n}}{{pp}_{1}}}} & (9)\end{matrix}$

Stage2: In order for the harmonic of order (pp₂+1) to couple with thefield of the magnets 1136 on the output rotor 1134, which rotates with aspeed of ω_(out), the following equation must hold:

(ω_(in) +pp ₂ω_(m))=(pp ₂+1)ω_(out)  (10)

which results in

$\begin{matrix}{\omega_{out} = {{\frac{1}{\left( {{pp}_{2} + 1} \right)}\omega_{i\; n}} + {\frac{{pp}_{2}}{\left( {{pp}_{2} + 1} \right)}\omega_{m}}}} & (11)\end{matrix}$

Overall Gear Ratio:

Combining equations (9) and (11) results in the overall gear ratio ofthe 2-stage harmonic gear given by equation (12)

$\begin{matrix}{\omega_{out} = {{- \frac{\frac{{pp}_{2}}{{pp}_{1}} - 1}{\left( {{pp}_{2} + 1} \right)}}\omega_{i\; n}}} & (12)\end{matrix}$

An embodiment of a magnetic gear as depicted in FIG. 11 was realisedusing the parameters of table 3 below. It can be appreciated from theeccentricity value and the minimum air gap value that the maximum airgap value is 6 mm.

TABLE 3 Values of parameters for the harmonic gear of FIG. 11. ParameterDescription Value e eccentricity (distance between centres of 5 mmhigh-speed rotor and stator) pp₁ Number of pole-pairs on intermediary 20rotor in stage 1 qq₁ Number of pole-pairs on stator 21 pp₂ Number ofpole-pairs on intermediary 21 rotor in stage 2 qq₂ Number of pole-pairson output rotor 22 Ro Outer radius 85 Gap_min Minimal length of air-gap1 mm Lpm Magnet thickness 5 mm Liron Thickness of back-iron 5 mm

The gear ratios related to the harmonic gear with the parameters givenin table 3 are shown in table 4.

TABLE 4 Gear ratios of harmonic gear G₁ Gear ratio of 1^(st) stage ofgear, ω_(in)/ω_(in) 20 G₂ Overall gear ratio of harmonic gear,ω_(in)/ω_(out) 440

It can be appreciated that relatively high gear ratios can be realised.

Referring to the first stage 1102 of the magnetic gear 1100 of FIG. 11,the shaft 1120 and the intermediary rotor 1116 rotate in oppositedirections. Therefore, an anticlockwise rotation of the shaft 1120results in a clockwise rotation of the intermediary rotor 1116 and visaversa. This rotation is demonstrated schematically by FIGS. 12( a) to12(d). Referring to FIG. 12( a), two permanent magnets 1202 and 1204 areidentified as reference points. They are associated with theintermediary rotor 1116 and the stator 1118 respectively. Thesepermanent magnets are arbitrarily selected as being aligned at 0° priorto rotation of the shaft 1120. The mutual positions of the two permanentmagnets 1202 and 1204 can be seen to have changed slightly when theshaft has been rotated 90° anticlockwise such that the permanent magnet1202 of the intermediary rotor 1116 has moved slightly in the clockwisedirection relative to the permanent magnet 1204 of the stator 1118 ascan be appreciated from FIG. 12( b). Referring to FIG. 12( c), the shaft1120 has rotated through 180° and the permanent magnet 1202 of theintermediary rotor 1116 has moved even further away in a clockwisedirection from the permanent magnet 1204 of the stator 1118. Referringto FIG. 12( d), the shaft 1120 has rotated through 261° and thepermanent magnet 1202 of the intermediary rotor 1116 has moved stillfurther away in a clockwise direction from the permanent magnet 1204 ofthe stator 1118.

A mathematical model of the first stage 1102 of the magnetic gear 1100of FIG. 11 was produced and simulations of the variations in the magnetfields were investigated. FIG. 13 illustrates circumferential variationof the normal flux density due to movement of the intermediary rotor1116 for a given point at the centre of a stator magnet such as theabove described stator magnet 1204. It can be appreciated that theintermediary rotor 1116 that is eccentrically positioned relative to thestator axis 1124 results in a varying air gap, which, in turn, resultsin a complex spatially distributed magnetic field 1302 that enablesmagnetic coupling/torque transmission between the permanent magnets 1126and 1130.

FIG. 14 illustrates the magnetic harmonic spectrum 1400 of the waveform1302 depicted in FIG. 13. It can be appreciated that the 21st harmonic1402 is dominant. Referring to the second stage 1104 of the magneticgear 1100 of FIG. 11, the shaft 1120 and the intermediary rotor 1116rotate in opposite directions and the intermediary rotor 1116 and theoutput rotor 1134 rotate in the same direction but at different rates ofrotation, that is, in a geared manner. Therefore, an anticlockwiserotation of the shaft 1120 results in a clockwise rotation of theintermediary rotor 1116 and the output rotor 1134 and visa versa. Thisrotation is demonstrated schematically by FIGS. 15( a) to 15(d).

Referring to FIG. 15( a), two permanent magnets 1502 and 1504 areidentified as reference points. They are associated with theintermediary rotor 1116 and the output rotor 1134 respectively. Thesepermanent magnets are arbitrarily selected as being aligned at 0′ priorto rotation of the shaft 1120. The mutual positions of the two permanentmagnets 1502 and 1504 can be seen to have changed slightly when theshaft has been rotated 261° anticlockwise such that the permanent magnet1502 of the intermediary rotor 1116 has moved clockwise to a greaterextent than the permanent magnet 1504 of the output rotor 1134 has movedclockwise as can be appreciated from FIG. 15( b). Referring to FIG. 15(c), the shaft 1120 has rotated through 2781′ and the permanent magnet1502 of the intermediary rotor 1116 has moved even further in aclockwise direction as compared to the permanent magnet 1504 of theoutput rotor 1134. Referring to FIG. 15( d), the shaft 1120 has rotatedthrough 5661′ and the permanent magnet 1502 of the intermediary rotor1116 has moved still further in a clockwise direction as compared to thepermanent magnet 1504 of the output rotor 1134. It can be appreciatedthat the gearing between the rotation of the input shaft 1120 and therotation of the output rotor 1134 is extremely large to the extent thatthe output rotor 1134 has rotated about 5° as compared to the 5661° ofrotation of the input shaft 1120. Therefore, extremely high and precisegearing can be realised using embodiments of the present invention.

Also, although the above embodiments have been described with referenceto radial field rotors and rotation, embodiments can equally well berealised using axial field rotors and rotation as well as translatorsand translation, that is, the principles of embodiments of the presentinvention can be realised in the context of linear gears.

The above embodiments have been described with reference to the innerrotor driving the outer rotors. However, it will be appreciated thatembodiments can be realised in which an outer rotor drives an innerrotor thereby reversing the gear ratio.

1. A magnetic gear comprising first and second moveable members havingassociated first and second pluralities of permanent magnetsrespectively arranged such that the first and second pluralities ofpermanent magnets are separated by a spatially varying airgap thatmodulates the fields of both of pluralities of permanent magnetsresulting in asynchronous harmonics that produce magnetic couplingtherebetween in a geared manner.
 2. A magnetic gear as claimed in claim1 in which the first moveable member comprises a flexibly deformablesubstrate bearing the first plurality of permanent magnetic that isdeformable by at least one of the shape and rotation of a respectiverotor.
 3. A magnetic gear as claimed in any preceding claim in which thefirst and second moveable members are mounted eccentrically relative toone another.
 4. A magnetic gear as claimed in any preceding claim inwhich the first moveable member bears a non-circular profile such thatmovement thereof induces an oscillatory motion of the permanent magnetsof the first plurality of permanent magnets.
 5. A magnetic gear asclaimed in claim 4 in which first moveable member comprises annon-circular rotor.
 6. A magnetic gear as claimed in any preceding claimin which the first and second moveable members are rotatable members. 7.A magnetic gear as claimed in claim 6 in which the first and secondpluralities of moveable magnets are rotatable about respectivenon-collinear axes.
 8. A magnetic gear as claimed in any preceding claimin which the first and second moveable members comprise translatablemembers.
 9. A magnetic gear substantially as described herein withreference to and/or illustrated in FIGS. 3 to 19 of the accompanyingdrawings.
 10. A magnetic gear comprising a non-circular high speed rotorand a flexible sheath having disposed therebetween a plurality ofbearings to support relative rotation between the high speed rotor andthe flexible sheath; the flexible sheath bearing a first plurality ofpermanent magnets arranged to magnetically couple, in a geared manner,with a second plurality of permanent magnets via asynchronous harmonicsgenerated in the magnetic fields of the first and second pluralities ofpermanent magnets as a result of a varying air gap between the first andsecond pluralities of permanent magnets.
 11. A magnetic gear as claimedin any preceding claim wherein the first moveable member (1136)comprises a third plurality of permanent magnets (1126) and the gearcomprises a stator (1318) bearing a fourth plurality of permanentmagnets (1130) third and fourth pluralities of permanent magnets areseparated by a spatially varying air gap that modulates the fields ofboth of the third and fourth pluralities of permanent magnets resultingin asynchronous harmonics that produce magnetic coupling therebetween ina geared manner.
 12. A magnetic gear as claimed in claim any precedingclaim in which the first moveable member is arrange to rotate about afirst axis (1122) of a shaft (1120) and the second moveable member isrotatable about a second axis (1124); the first (1122) axis beingarranged to precess about the second (1124) axis.
 13. A magnetic gear asclaimed in any preceding claim in which the first moveable element(1116) is eccentrically moveable relative to a stator (1118) androtatable about a first axis (1122).
 14. A magnetic gear as claimed inclaim 13 in which the first axis (1122) is arranged to orbit a secondaxis (1124).
 15. A magnetic gear as claimed in any preceding claim inwhich the varying distance is given by r=r_(av)+r_(b)·cos(nnθ), wherer_(av), is the average radius and r_(b) is the maximum deviation fromthe average and nn is an integer. A method of generating a magneticfield having asynchronous harmonics to couple first and second sets ofpermanent magnets separated by a varying distance. A method of spatiallymodulating magnetic fields using a varying air gap between first andsecond pluralities of permanent magnets, which enables magneticcoupling/torque transmission between the first and second pluralities ofpermanent magnets.
 16. A method of generating a magnetic fieldsubstantially as described herein with reference to and/or asillustrated in FIGS. 3 to 15( d) of the drawings.